Abraders, abrasive particles and methods for producing same

ABSTRACT

Abraders are formed from encapsulated abrasive particles which are uniformly distributed in a matrix. Superior abraders may be formed by metal bonding such encapsulated abrasives with a metal matrix which forms a continuous phase in which the abrasive particles may be positioned. Where the abrader is formed from a mixture of the bonding metal and a single type of abrasive particle, the specific gravity of the abrasive particle may be adjusted to match more closely that of the metal. The encapsulated abrasive particle may form the primary abrasive together with a secondary abrasive which is not as hard as the primary abrasive and which may or may not be encapsulated with a metal. Where a plurality of abrasive particles of differing specific gravity are used, one or the other or both may be adjusted in density by employing an encapsulating metal of suitable specific gravity. Abrasive particles are improved in function as abrasives, in addition to having the specific gravity adjusted by encapsulating them with a metallic envelope; preferably the envelope is made of a pure metal in dendritic crystalline form. Desirably the abrasive substrate is placed in contraction by the envelope which is heat shrunk onto the abrasive substrate. The preferred method is to deposit the metal on the substrate at an elevated temperature by contacting a vapor of the metallic compound with the substrate particle under reducing conditions. The preferred primary abrasive is a diamond, and it is preferably etched before coating.

United States Patent 1 Wilder et al.

5] Oct. 15, 1974 1 ABRADERS, ABRASIVE PARTICLES AND METHODS FORPRODUCING SAME [75] Inventors: Arthur G. Wilder; Harold C.

Bridwell, both of Salt Lake City, Utah [73] Assignee: ChristensenDiamond Products Company, Salt Lake City, Utah [22] Filed: Jan. 24, 1972[21] Appl. No.: 220,351

[52] U.S. Cl 51/295, 51/307, 51/309 [51] Int. Cl B24d 3/06 [58] Field ofSearch 51/293, 295, 307, 309

[56] References Cited UNITED STATES PATENTS 3,293,012 12/1966 Smiley etal. 51/295 3,574,579 4/1971 Clarke 51/309 3,650,714 3/1972 Farkas 51/2953,650,715 3/1972 Brushek et al.... 51/309, 3,664,819 5/1972 Sioui et a151/295 Primary Examiner-Dona1d]. Arnold Attorney, Agent, or Firm-BernardKriegel [57] ABSTRACT Abraders are formed from encapsulated abrasive particles which are uniformly distributed in a matrix. Superior abradersmay be formed by metal bonding such encapsulated abrasives with a metalmatrix which forms a continuous phase in which the abrasive particlesmay be positioned. Where the abrader is formed from a mixture of thebonding metal and a single type of abrasive particle, the specificgravity of the abrasive particle may be adjusted to match more closelythat of the metal. The encapsulated abrasive particle may form theprimary abrasive together with a secondary abrasive which is not as hardas the primary abrasive and which may or may not be encapsulated with ametal.

Where a plurality of abrasive particles of difiering specific gravityare used, one or the other or both may be adjusted in density byemploying an encapsulating metal of suitable specific gravity.

Abrasive particles are improved in function as abrasives, in addition tohaving the specific gravity adjusted by encapsulating them with ametallic envelope; preferably the envelope is made of a pure metal indendritic crystalline form. Desirably the abrasive substrate is placedin contraction by the envelope which is heat shrunk onto the abrasivesubstrate. The preferred method is to deposit the metal on the substrateat an elevated temperature by contacting a vapor of the metalliccompound with the substrate particle .under reducing conditions. Thepreferred primary abrasive is a diamond, and it is preferably etchedbefore coating.

24 Claims, 12 Drawing Figures PATENIEUHm 1 5mm SHEET 10F 6 AssolzsarzTHERMOCOUPLE BUBBLE TlzAPs Tu 5E FUQMAQLE FLUID Be D QEACTOIZ To DEAERA-ra --rvAauum Pump (D 7 FLOW Me're as I PALLADIUM CATA LYSTPATENIEBHCTISIQH i I SHEET 20F 6 PAIENTEB 3.8414852 SHEET 30F 6 loia.a4-1'.e52

PATENTEDUCT 1 5 I974 SHEET 5 OF 6- This invention relates to abradersformed of a plural ity of different abrasive particles bonded in acontinuous phase matrix.

Abrasive, grinding, cutting and earthboring tools, hereinafter referredto as abraders, have bound abrasivc particles into an abrader structure,using a binder such as an organic polymer resin and, in some cases,metal, which acts as the matrix to hold the abrasive particles in thcabrader structure.

In one form of the above structures, a plurality of different abrasiveparticles are employed. In addition to particles of high hardness valueswhich act as the primary abraders, there is distributed in thecontinuous phase of the metal matrix binder a secondary abrasive oflower hardness value.

The purpose of the secondary abrasive particles is to wear awaypreferentially thus exposing new abrasive faces of the primary abrasiveparticles.

It is desirable in such structures that the primary abrasive and thesecondaryabrasive be uniforrnally distributed throughout the matrix. Ifthe primary abrasive is not uniformally distributed, the abraderstructure will not be uniformally worn away and the result will be thatat wearing areas of high concentrations of primary abrasive the abraderwears away less than in the area of low primary abrasives concentration.

The accelerated erosion of the secondary abrasive particle and theaccompanying local wearing away of the bonding matrix results in alarger loading on the areas of higher primary abrasive particleconcentration since the abrader structure will ride up on these areas.The load being concentrated on these reduced areas causes an increasedload per unit area on the localized pressure areas and on the underlyingabrader structure, such as a saw blade on which the abrader structuremay be mounted.

In some cases, this increased load may fracture the primary abrasive andcause it to be torn out of the ma: trix resulting in excessive wear.

In such cases, the cutting rate may not be uniform and it is necessaryto either reduce the loading or the cutting rate.

We have been able to overcome to a larger measure. these disadvantagesby providing for a more uniform distribution in the matrix of theprimary and if used of the secondary abrasive particles to obtain acontrolled and substantially uniform spacial distribution of primary andif used of the secondary abrasive.

In such cases, it is possible to select a concentration of primary andif used of secondary abrasive to provide a suitable spacing between theparticles to provide sufficient pore volume to give a desirable bond anda sufficient mass of matrix to hold the abrasive particles in position.

This invention provides for the aforementioned uniform distribuition ofthe primary and secondary abrasive if used by first forming an intimatemixture of particles of the primary and secondary abrasive in which theparticles are as closely as is practically feasible of substantially thesame density. Additionally, the uniformity may also be reinforced byusing all particles in the same mesh size range and using them in asnarrow a mesh size range as is practically convenient.

In such case, by suitable mixing of the particles the bring theresultant densities of all of the primary and secondary particles to asnearly the same density as is conveniently feasible, i.e., that all ofthe particles have substantially the same density.

Where the abrader structure is to be used as a cutter or abrader, forexample in oil well drill bits or other boring, shaping tools or sawssuitable, for example, in sawing concrete, masonry, rocks, ceramics,bricks,

etc., we prefer to use abrasive materials, preferably .those havinghardness in excess of about 2,500 kg/mm (Knoop or Vickers) and theharder the better. An additional useful criteria is that thc abrasivematerial should have a melting or softening point in excess of thehighest tempterature reached in the process by which the abraderstructure is formed, such as is described hereinbelow.

We prefer to employ, because of their physical prop-- erties, such ashardness, melting point, chemical'stability, and other physicalproperties, one of the following abrasive material, preferring amongthem diamonds, either natural or synthetic. In addition to diamonds, wemay use any one of the following abrasive particles shown in Table l.The values reported in the table are taken from the availableliterature.

As described above, we wish to select as the primary abrasive, onehaving a substantially higher hardness value than that of the secondaryabrasive particle.

Table 1 lists suitable materials from which may be chosen the primaryand accompanying similar abra- SlVeS.

TABLE 1 MP. C. Sp.G. Percent Hardness Linear Coeff. kg/rnm of ExpansionKnoop* X 10 Vickers" 0-1 000 F.

Diamonds (Synthetic or Natural) 3.5 1.5 8000* Aluminum Oxide (M 0 20603.54 4.4 3000* Cast Eutectic Tungsten Carbide 4800 I5 Tungsten MonoCarbide (WC) 4800 15.8 2.7 Ditungsten Carbide (W C) 4800 l7.3 WOO-2400TABLE l Continued M.P. C. Sp.G. Percent Hardness Linear Coeff. kg/mm ofExpansion Knoop* X Vickers** 0-1000 F.

Boron Nitride (Cubic) I7OO 3.48 4700* Tetrachromium Carbide (Cr..C) 15006.99 3 Trichromium Dicarbide (Cr C,) i910 6.68 2.4 2650 TitaniumDiboride (TiB,) 2870 4.52 4.2 MOO-3500* Hafnium Diboride (HfB 3250 11.204.2 3800* Zirconium Diboride (ZrB 3100 6.09 4.6 2000* Calcium Hexaboride(Cam) 4050 2.46 3.6 2740: 220* Barium Hexaboride (BaB.,) 4100 4.32 3.83000: 290 Tantalum Carbide (TaC) 3.7 Silicon Carbide 1000 3.2] 2.4IZOD-2900* nae method of encapsulation where a nonrnet allic matrix isto be employed, for example, where an or; ganic polymer resin isemployed we may deposit the: metal of higher specific gravity in anyconventional method, such as electrochemical or electrolytic methods andconventional handbooks will list such metals. Where, however, we wish toemploy a metal as the matrix and apply the metal in molten condition tothe mixed particles, we prefer to use metals as the envelope having asuitably high melting point and other physical properties. Table 2 listssuch metals.

It will be observed that there is a substantial disparity in specificgravity between the various abrasive parti cles. In order to match thedensity of the selected parti cles more closely, we encapsulate theparticles of lower specific gravity with a metal having a differentspecific gravity so as to bring the apparent densities of the severalparticles more closely to the same value.

The totalweight of the particles is increased and as the increase involume of the particles is the less the greater is the densitiy of theenvelope and vice versa. Since the metal envelope is chosen so that thespecific gravity of the metal envelope be greater or less than that ofthe underlying substrate particle, the density of the composite coatedparticles is increased or decreased.

The effect of the densities of the particles and of the coat will appearfrom the following. if x be the weight percent of the substrateparticles in the coated particle and d, is the density of the substrateand d be the density of the envelope and d is the density of the coatedparticle, then d [d x d,( l00-x)]= l0Od,d

""Th'e'accorhpanying secondary Creamery abrasive i particle may or maynot be coated and may be chosen to match the particle size ofaccompanying particle.

weprfaiifirafia a '5' Saarinen-teenagerto employ as encapsulatingmetals, those listed in Table 2. The values are obtained from availableliterature.

The encapsulation of the abrasive particles with a metallic envelopeaccording to our invention has values in addition to permitting of auniform distribution of the particles as described above.

Where metal is used as a matrix to bind the abrasive particles in theabarader structure, encapsulation of the abrasive particles increasesthe grip of the metal matrix on the abrasive particle. Where the bond isweak, the particles are torn out of the metal matrix, causing excessivewear.

The interrnetallic bond between the metal matrix and the primary orsecondary abrasive increases the retention of the abrasive particleuntil its cutting life is ended by wearing away of the particle orbreaking away of fragments thereof from the portion of the abrasiveparticle which has become free of the encapsulation at the fer from theabrasive particle resulting from the more intimate contact surfacebetween the envelope and the substrate particle and the envelope and themetal matrix. Heat generated at the abrading surfaces, if not readilytransmitted to and absorbed in the metal matrix, acting as a heat sink,will cause a local rise in temperature which may have a deleteriouseffect upon the life of the abrasive particle.

In order to obtain the adjusted apparent density as well as theincreased bond between the abrasive particles and the metal matrix, anyconvenient method for deposit of the metal envelope on the particlesubstrate may be employed. Thus electrochemical or electrolytic methodswhich have been previously employed in coating abrasive particles foruse in abrader structure with organic resin will permit of someadjustment of the apparent density of the coated particle. They willalso, when used together with a metal bonding agent in our novel abraderstructure, result in an improved bond between the metal matrix and thecoated particle, due to the improved wetting by the molten metal.

The use of the coated particle in a composite structure employing ametal matrix is an improvement over the use of an abrasive particlecoated by an electrochemical or electrolytic process where used with aresin binder. It is similarly an improvement over the use of uncoatedabrasive particles with resin or metal binders acting as a matrix forthe abrasive particles.

Abrasive particles coated by procedures such as electrochemical andelectrolytic processes may result in deposits which are contaminated byintergranular inclusions of impurities from their aqueous environment.Furthermore, the deposits particularly in the case of electrolyticdeposits have intergranular planes of weakness and the coating has arelatively low tensile and bending strength. They thus do not improve inany substantial degree the physical properties of the coated particle ascompared with the uncoated particle.

We prefer that the metal envelopes which constitute the abrasiveparticles of our invention employed in the novel abrader structure ofour invention differ from the foregoing coatings in composition andcrystalline nature.

We prefer to form the metal envelope by a process in which the abrasiveparticle is coated by means which deposit metal on the abrasive ofmaterials which is substantially free of intergranular impurities.

The deposits according to our preferred procedure constitute a puremetal envelope substantially free of intergranular inclusions.

The preferred metallic envelope is formed of allotrimorphic crystaldendrite grains which start at and extend from the substrate surface instatistical orientation We have also found it useful, where the chemicalnature of the abrasive particle substrate permits, to choose metallicenvelopes which form a surface chemical bond with the substrate byreason of a limited chemical reaction between the metal and thesubstrate surface, thus producing an encapsulated particle in the formof a cermet.

The formation of the intersurface bond between the envelope and thesubstrate is facilitated by the elevated temperature employed in ourpreferred method of metal deposition.

Where the metal envelope has a coefficient of ther- This property has anadvantage irrespective of the bonding agent employed and mayadvantageously be used whether resin or metal acts as the bonding agent.

In order to obtain a compressive force on the substrate, we select ametal for the envelope having a substantially greater coefficient ofexpansion than the substrate. In such case, when the metal is depositedon the substrate at an elevated deposition temperature, on cooling, themetal sheath will contract more than the substrate, putting thesubstrate under compression. Since the linear coefficient of thermalexpansion of suitable abrasives are in the range of about I to about 5 X10* inches per inch per degree Fahrenheit, we select metal sheathshaving a higher coefficient of expansion than the substrate. Forexample, we select metals having linear coefficients of expansion ofabout 2 X l0" to about 10 inches per inch per degree Fahrenheit. Bymatching the coefficients of expansion, as described above, a usefulencapsulation may be obtained. It is useful to remember that thecoefficients of cubic expansion may, for the above purposes, be taken asabout three times the linear coefficient of expansion. In such acombination the distruptive force sufficient to fragment the substrateparticle must be greater than that which would fracture theunencapuslated particle, since it must overcome initially thecompressive force "which places the underlying substrate in compression.

Thus, for example, if diamond be the substrate, we may use for thepurpose any one of the metals listed in Table 2 to form theencapsulating envelope and thereby also increase the apparent density.In each of these cases, the coefficient of linear expansion of the metalis substantially greater than that of diamond, and their use would havethe advantage of adding a compressive force upon the diamonds to help inovercoming the tensile forces which would tend to fracture the diamondwhen used in an abrader structure as the abrasive particle.

In selecting the encapsulating metal with the view of obtaining theadvantage of the differential contraction, metals may be selected,depending on the stress desired to be imparted, for example, for themetals listed in Table 2 and the abrasives of Table 1, metals having acoefficient greater than the substrate coefficient by about to percentor more of the value of the coefficient of the substrate. That is, thecoefficient of the metal should be about 1.05 or more, for example, upto about seven times the coefficient of the substrate.

In selecting the metal encapsulating material, when employing diamondsas a substrate, when we employ carbide-forming metals, we prefer toemploy those which have only a limited reaction rate at the temperaturesof deposition, as hereinafter described. For example, we may usemolybdenum, tungsten, tantalum, titanium and niobium, all of which arecarbide formers but are unlike iron which under the conditions ofdeposition or the production of the abrader may result in excessiveattack on the diamond.

For all of the foregoing reasons, we prefer to use in combination withthe abrasive particles tabulated in Table 1 above, and selectedaccording to their properties as described above, tungsten, tantalum,niobium (columbium) and molybdenum, and, among the primary abrasiveparticles, we prefer to employ diamonds, either the natural or syntheticforms, and prefer to employ tungsten as the encapsulating material,deposited under conditions to produce pure tungsten of the crystal formas described herein.

Where we employ the metal encapsulated abrasive in abrader structuresformed by metal bonding the encapsulated abrasive in a metal continuousphase matrix, we prefer to employ as a bonding agent a metal having asignificantly lower melting point than the metal sheath of the abrasivesubstrate. When employing diamonds as the encapsulated abrasiveparticles, we prefer to limit the melting point of the metal matrix to atemperature below about 2,800 F. in order not to expose the diamonds toexcessive temperature which may impair the mechanical strength of thediamonds.

Another important consideration is the coefficient of thermal expansionof the metal matrix used as bonding agent. Since, in general, the lowmelting metals and materials have a high thermal expansion, in theabsence of an encapsulating metal which is wetted by the molten metal,the mass of matrix on cooling would tend to pull away from the abrasivematerial, thus impairing the bond. It is one advantage of theencapsulating metal that the thermal expansion of the metal sheathmatches more closely the thermal expansion of the metal matrix and thatthe interfacial tensions will tend to prevent the pulling away of themetal matrix from the metal sheath. Such metals having melting points soas to be fluid-in the formation of the abrader structure, for example,at temperatures below about 2,800 F. when employing diamonds aresuitable.

However, we prefer to employ such metals which also have the preferredproperties as hereinafter de-'- scribed. The metal chosen should befluid at the temperature at which it is desired to employ the moltenmetal in forming the composite abrader structure and desirably shouldhave, when. solid, ductility as measured in the terms of micro-hardnessof below about 400 kglmm Desirably, also, it should have a compressivestrength above about 150,000 p.s.i., a transverse rupture strength aboveabout 90,000 p.s.i. and an impact strength above about 5 foot pounds.

For this purpose we may use copper-based alloys such as brass and bronzealloys and copper-based alloys containing various amounts of nickel,cobalt, tin, zinc, manganese, iron and silver.

Since when using encapsulated diamonds the diamond is protected fromattack by the metal. we may use cobalt-based, nickel-based, andiron-based alloys of suitable properties. These alloys are excluded fromuse as metal matrixes when using unencapsulated diamonds because undermolten conditions they attack the diamond excessively. Thus we may withthe encapsulated diamond, for example, employ thenickel-copper-aluminum-silicon alloy having a melting point below 2,000F.; cast iron, cobalt, chromium, and tungsten alloys having meltingpoints below about 2,800 F. may be used.

Where the abrasive particle is a tungsten carbide or diamond particlewhich is attacked by nickel, cobalt or iron-based alloys, theencapsulation of the tungsten carbide or diamond by a metal envelope ofsubstantially higher melting point according to our invention willprevent the attack which the unencapsulated particle would otherwisesuffer under the conditions of fabrication of the abrader structure.

The procedure we prefer because it produces the superior envelope whenapplied to produce our novel encapsulated abrasive particle is theconversion of a volatile compound of the metal into the metal depositedon the substrate and a gaseous or vaporous reaction product which may beremoved from contact with the encapsulated metal. This leaves anenvelope substantially free of included impurities.

For this purpose we prefer to use the halides or the carbonyls of themetals. Preferably for convenience of operation, we prefer to employthose compounds having a boiling point at atmospheric pressure below thereaction temperature.

While compounds which may be placed in the liquid state and which may bedistilled by vacuum distillation or by reduction of their partialpressure by means of a carrier gas are possible, the compounds listed inTable 3, having reasonable boiling points,- so that their volatilizationmay be conveniently allowed are preferred by us. i

TABLE 3 B.P.C. at 760 mm.

Iron Carbonyl [Fe(CO)6] l02.8+ Molybdenum Pentachloride [MoC1 268Molybdenum Hexafluoride {Moi- 35 Molybdenum Carbonyl [Mo(CO) 156.4Tungsten Pentabromide [WBr I 333 Tungsten Hexabromide [WBr 17.5 TungstenPentachloride [WCl 275.6

, Tungsten Hexachloride [WCI 346.7

Tungsten Carbonyl [W(CO) at 766 mm. Tantalum Pentachloride [TaCl 242Tantalum Pentafluoride [Tall] 229.5 Titanium Tetraboride [TiBrd 230Titanium Hexafluoride ITiF 35.5 Titanium Tetrachloride [TiCh] 136.4Columbium Pentabromide [CbBr 361.6 Columbium Pentafluotide [CbF 1 236Columbium Pentachloride [CbCl 236 Nickel Hexafluoride (NiF l 4 at 25 mm.Vanadium Tetrachloride [VaCL] 148+ Vanadium Pentafluoride [VaCl I 1.1 1+

Unless otherwise indicated In view of the above consideration, we preferto employ tungsten as an encapsulating metal because of its high densityand high melting point (See Table 2). It gives under the conditions offabrication according to our invention a coating of exceptional highstrength. It is readily wetted by the molten metal matrixes describedabove and forms a strong metallurgical bond with the metal matrixesemployed in our invention. It is particularly useful where the substrateis diamond or other substrates which will react with the tungsten suchas those which form cermets with tungsten.

Our preferred primary abrasive is diamond. Where encasulated with ametal under the preferred conditions as described herein, it willproduce a superior abrader structure of longer life. Where encapsulatedwith tungsten or other suitable metals as described above, it will afterthe exposed metal sheath in contact with the work has been worn away beexposed to the work but will otherwise be gripped by the encapsulatingenvelope which is in turn gripped by the metal matrix.

In place of or in addition to the encapsulated diamond, we may use theother abrasives as described above, preferring among them encapsulatedalumina but may also use the other abrasives described above,particularly encapsulated tungsten carbide or silicon carbide as is morefully described below.

The invention will be further described by reference to the followingfigures:

FIG. 1 is a diagrammatic flow sheet of our preferred process ofencapsulation. FIG. 2 is a section through a mold for use in theinfiltrant technique of forming abraders according to one form of ourinvention.

FIG. is a sectional view taken on 5-5 of FIG. 2.

FIG. 3 is a schematic showing of a mold for use in a hot press techniqueemployed in forming an abrader element.

FIG. 4 is a sectional view taken on line 44 of FIG. 3.

FIG. 6 shows one application of a shaped abrader according to ourinvention to a saw.

FIGS. 7-12 are photomicrographs of an etched section of a coatedabrasive particle contained in a metal matrix according to ourinvention.

FIG. 1 illustrated a flow sheet of our preferred process for producingthe novel encapsulated abrasive of our invention. The particles to becoated are placed in the reactor 1, whose cap 2 has been removed. Thereactor has a perforated bottom to support the particles of selectedmesh size. With cap 2 replaced and the valves 3, 4, 5, and 13 closed,and with valve 7 open, the vacuum pump is started to de-aerate thesystem. Valve 7 is closed and the system is back filled with hydrogenfrom hydrogen storage lll, valve 5 being open.

The reactor is heated by the furnace 9 to the reaction temperature, forexample, from about l,000 to about 1,200F. while purging slowly withhydrogen. The hydrogen flow rate is increased until a fluidized bed isestablished. Hydrogen prior to inroduction into the reactor passesthrough a conventional palladium catalyst to remove any impurities, subhas oxygen in the hydrogen. Vaporized metallic compound is dischargedfrom the vaporizing chamber 10, which may if necessary be heated byfurnace 14, together with an inert gas, for example, argon from argonstorage 6 into the reaction chamber.

Preferably we desire to employ the volatile metal halides referred toabove, although, in some cases, we may use the carbonyls listed in Table3. Where the halide is employed, the reaction forms hydrogen halide,which is passed through the bubble traps and is absorbed in theabsorber. Where the volatile compound employed is a fluoride, theproduct formed is a hydrogen fluoridc. and we may use sodium fluoridefor that absorption. We prefer to employ hydrogen in stoichiometricexcess.

The reaction deposits metal on the substrate and the effluent material,being in the vapor state is discharged, leaving no contaminants on or inthe metal. The metal is formed in its pure state.

The rate of metal deposition depends on the temperature, and flow rateof the reactants, being the greater the higher the temperature and thegreater the flow rate of the hydrogen and volatile metals compound.

After the deposit is formed, the valves 4 and 5 are closed and argon iscontinued to pass into the reactor and the metal encapsulated abrasiveis allowed to cool to room temperature in the non-oxidizing condition ofthe argon environment.

The conditions in the reactor, both because of the mesh size andparticle size distribution of the particles and because of the velocityof the vapors and gases fluidizes the particles. As will be recognizedby those skilled in the art, a dense phase is established in the lowerpart of the reactor in which the particles are more or less uniformallydistributed in violent agitation in the dense phase. This results in asubstantially uniform deposit perunit of surface of the particles.

The reaction products and the carrier gases and excess hydrogen enterthe upper space termed the disengaging space where they are separatedfrom any entrained particles.

Where the diamond particle is smooth as, for example, in the case ofsnythetic diamonds, we may improve the bond of the metal envelope to thesubstrate diamond surface produced in the process described above byfirst surface etching of the diamond. The etching of the diamonds willalso have an advantage where the metal envelope is produced by otherprocesses such as electrochemical or electrolytic deposition methods.However, for the reasons previously described, the product produced bythe process of vapor deposition described above is superior and ispreferred by us.

EXAMPLE I To etch the diamonds, we immerse them in a molten bath of analkali metal nitrate or alkaline earth nitrate at a temperature belowthe decomposition temperature; thus in using potassium nitrate,temperature would range from 630+ F. and under 750 F.; sodium nitrate,about 580 F. and under about 700 F.; barium nitrate, at or above 1,100F. and below its decomposition temperaure. We prefer to employ potassiumnitrate at about 630 F. for about an hour. The bath is contained in anitrogen or other inert gas atmosphere.

At the completion of the heating process, the molten bath is cooled andthe cooled bath is then leached with water to dissolve the salt, leavingthe etched diamonds which may then be separated and dried.

The degree of etching depends upon the immersion time and a suitabletime will be about an hour under which conditions the particles willlose from about /2 to 2 percent of their weight. The surface of thediamonds is roughened and pitted and forms a desirable and improvedsubstrate base.

For purposes of illustration, not as limitations of our invention, thefollowing examples are illustrative of the EXAMPLE 2 Diamonds, eithersynthetic or natural. preferably etched as above, of mesh size suitablefor fluidizing are introduced into the reactor 1. The actual mesh sizeemployed depends upon the service to which the abrader is to be placed.For use in oil well tools, cutters, saws, and grinders, we may useparticles of size (Tyler mesh) through a 16 and a 400 mesh (-16 400).Preferably we employ 50 to 100 mesh material, for example, 40 50 mesh.in depositing tungsten, we may and prefer to employ tungstenhexafluoride, which is contained and vaporized in 10. it is volatile atatmospheric temperatures and need not be heated. In the reactor employedafter the system has been de-aerated and back filled, hydrogen flow isestablished at a low flow rate of about 100 ml/min and as describedabove, the temperatures in the reactor 1 having been adjusted to 1,150E, as measured by the thermocouples, the hydrogen flow is increased toabout 1,2001,350 ml/min, and the flow of the tungsten fluoride vapor toabout 150 ml/min and the argon gas is adjusted to about 285 ml/min, allas measured by the flow meters as indicated in FIG. 1, the hydrogenbeing in stoichiometric excess over the tungsten hexafluoride.

The thickness of the coat of the tungsten on the diamond depends on theduration of the treatment and suitably for the 40 to 50 mesh diamondsdescribed above, the coat will be 1 mil. thick in about 1 hour. Suitablethickness deposit will run from about 0.1 to about 1 mil. thick.

The thickness of the coat will also determine the apparent density (d,,)of the particle as described above.

It will be seen that with the apparent density of the coated particlefor a diamond of 3.5 specific gravity and tungsten of 19.3 specificgravity we may obtain a tungsten coated diamond particle of apparentdensity a above 3.5 and below 19.3 depending on the weight percent ofthe tungsten deposited. As stated above, this may vary from an apparentdensity of 4 to an apparent density of 17 be depositing tungsten fromabout 14.65 percent of the weight of the coated particle for an apparentdensity of 4 to tungsten of a weight percent of 96.9 percent of thecoated particle for an apparent density of 17. For other densities, theformula given above will indicate the weight percent of the coatingmetal required to adjust the apparent density of the diamonds to thedesired amount by regulating the rate of reaction by adjusting thetemperature and the concentration of the reactants and duration oftreatment such desired deposits of encapsulating metal may be achieved.

EXAMPLE 3 Instead of diamonds, we may use alumina. The mesh size,temperature, and procedure as described in Example 1 may be followed toproduce a tungsten coat of the weight percent described. Since thealumina and diamonds are of analagous density, what has been stated withregard to the required weight percent (in the case of diamonds) of theencapsulating metal applies here as well.

EXAMPLE 4 Similarly, a tungsten carbide may be coated with tantalum toadjust the weight percent as has been described above, following theprocedure described in Example 1.

EXAMPLE 5 The process of Example 2 was employed in coating siliconcarbide particles of 80 100 mesh. The density of silicon carbideapproximates that of diamonds; what has been said of the requiredpercent of tungsten carbide to adjust the apparent density of the coateddiamonds applies as well to the silicon carbide.

In the above examples, the substrate surface is completely coated,indicating that the process of vacuum chemical vapor deposition hasgreat throwing power. The outer surface of the coated particles istopographically congruent to the outer surface of the underlyingsubstrate and reproduces it. The interlocked structure produces acoating of high tensile and bending strength. Since the coating isproduced at high temperature, on cooling the contraction of some 1,100F.will be substantially in excess of the contraction of the substrate asdescribed and the resultant eventual contraction will produce acompression of the underlying abrasive particle.

The metal coated particles may be employed in producing improved abraderstructures from mixtures of primary and secondary abrasives bytechniques previouslyused with such mixtures employing unencapsulatedabrasive particles. These include what have become known asinfiltration, hot pressing, and flame metallizing procedures.

in producing such abrader structures, we prefer for reasons previouslydescribed to adjust the apparent densities of the primary and secondaryabrasive particles.

Where the abrader is made up of a single type of abrasive particle, forexample, any of the suitable particles of Table 1 selected as describedabove and having a specific gravity less than the metal used as a matrixwhere the abrader is to be formed from a mixture of the abrasive andmetal powder, we may wish to adjust the specific gravity of the abrasiveto bring it more closely to that of the metal.

By encapsulating the abrasive of specific gravity different from themetal matrix with a metallic envelope of different specific gravity, wemay adjust the apparent density of the encapsulated abrasive toapproximate that of the metal matrix.

We can similarly by selecting the substrate and the coating metal andthe weight percent of the coat which is deposited obtain an abrasiveparticle of desired apparent density and match the densities of theprimary and secondary particles and the binder metal. For example, byadjusting the weight percent of the tungsten on the above diamonds toabout 61 percent, we can obtain a particle of about 7 grams/cc densityand by coating tungsten carbide with titanium to 54 percent by weight ofthe coated particle, we can obtain a particle about 7 grams/cc density,which will approach the specific gravity of suitable binder metal.

It may not always be necessary to equalize the apparent densities of theprimary and secondary particles or also that of the binder metal, ifdesired, for merely by approaching each other by encapsulation of one orthe other of the particles according to the principles previouslydescribed, an improved distribution of each of the particles may beobtained. For purposes of producing a uniform mixture of primary andsecondary abrasive particles. the apparent densities of the particles ofprimary and secondary abrasives may be adjusted so that the differencein the apparent densities after adjustment according to our inventionshall be equal to about 40 percent to 80 percent or less of thedifference in the specific gravity of the unencapsulated abrasives. Morepreferably we may reduce the difference between the particles to underabout 25 percent. Desirably we may produce particles of primary orsecondary abrasives of lowest apparent density of about 30 percent ormore and preferably 80 to 100 percent of the density of the particle ofhighest density by encapsulating one or the other or both of the primaryand secondary abrasive particles.

Thus, for example, a coat of tungsten metal (19.3 sp.g.) of about 98.7percent by weight of a coated diamond particle 3.5 sp.g. will match thespecific gravity of a eutectic carbide of specific gravity.

By coating the tungsten carbide with titanium sp.g. 4.54, we may reducethe apparent density of the tungsten carbide and thus require a lessercoat on the diamond particle to match.

By coating the tungsten carbide used, molybdenum or any of the othermetals listed in Table 2 having lower specific gravities reduce theapparent density of the coated particle.

Where the primary abrasive is diamond and the secondary abrasive istungsten carbide, we may use any of the metals listed in Table 2 toincrease the apparent density of the diamond particle to bring it moreclosely to the density of the particle of the secondary abrasive and thebinder metal if, for example, the hot press method is employed.

We prefer where the continuous phase of the matrix is metallic, in orderto obtain additional advantages, to employ as encapsulating metals,those listed in Table 2. The values are obtained from availableliterature.

The encapsulation of the abrasive particles with a metallic envelopeaccording to our invention has values in addition to permitting of auniform distribution of the particles as described above.

The secondary abrasive used in the above construction may be usefully atungsten carbide ranging from WC having 6.12 weight percent of carbon toW C having a carbon content about3. 16 weight percent. A useful materialis so-called sintered tungsten carbide and consists of microsized WCcrystals and cobalt metal bonded by liquid phase sintering at hightemperature. The cobalt content varies from 3 weight percent to overweight percent. This material has a hardness of about 1250 to 1350 kg/mm(Knoop). Another form of eutectic alloy containing about 4 percent byweight of carbon having a hardness in the range of 1,900 to 2,000 kg/mm(Knoop) may also be used.

EXAMPLE 6 FIGS. 2 and 5 show a suitable graphite mold for use with theinfiltrant technique for producing saw blade segments to be brazed to asaw blade. The mold is composed of a base 101, the mold proper 102, withan anchor 103, carrying a funnel 104, clamped by clamp bolt 105, andcovered with a furnace cap 106. The mold proper consists ofcircumferentially space mold cavities having substantially smallercircumferential extension than their radial length. The primaryabrasive, for example, a mix of tungsten encapsulated diamond particlcs20 45 or 45 60 screen having a density of about 7 and titaniumencapsulated powdered tungsten carbide with a density of about 7 istamped into the mold 102. The funnel contains a bronze-copper-tin alloypowder through a 200 mesh screen. The diamonds form about 25 percent byvolume of the mixture of metal and diamond finally formed in the moldcavity 103. The mold is heated to about 2,0002,100 F. to melt the alloywhich percolates through the interstices between the diamond particlesin the mold cavity, i.e. infiltrates the pores filling them to form thecontinuous phase binding the coated diamond particles and the tungstencarbide in the continuous metal matrix.

Tungsten carbide may be coated, for example, with molybdenum, tungsten,titanium or niobium. Preferably, however, we prefer to employ molybdenumor titanium or columbium and to encapsulate the secondary abrasive bythe process previously described.

The coated tungsten carbide may be replaced by coated secondary abrasiveas described above, for example, tungsten coated alumina or siliconcarbide. The

.metal envelope may be tungsten or any other metal chosen as describedabove.

Instead of employing the infiltrant process, we may employ a hot pressprocedure to formulate the abrader of our invention. In such procedure,the mixture in the mold is a mixture of abrasive particles and powderedmetal which is to form the continuous metal matrix to bond the abrasiveparticles.

EXAMPLE 7 The mold employed is shown in FIGS. 3 and 4. The mold issimilar to that of FIG. 2 except that no funnel is employed and the nutis now a plug 107 and the funnel 104 is replaced by the cap 108 in placeof cap 106. The mold is formed for the insertion of the cap as shown.The secondary abrasive may be coated abrasive as described in connectionwith Example 6.

To produce the saw blade element (See FIG. 6) according to the hot pressmethod described above, an intimate mixture of titanium encapsulatedtungsten carbide and tungsten coated diamond of -35 50 mesh which hasbeen coated with a tungsten metal envelope to a density of about 7 tomatch the density of the encapsulated tungsten carbide as describedabove and a -200 mesh bronze-tin alloy are tamped into the mold of FIGS.4 and 5. The concentration of diamonds in the mix may suitably be thesame as described in connection with Example 7. The mold is heated toabout 1,600F. at about 3,000 p.s.i. pressure to produce a saw bladeelement as described above.

For example, employing the procedures of Examples 7 and 8 in forming a12-inch saw blade on which about 19 of the above sections are brazed atthe periphery of the saw blade, sections of about l-7/8 inches long,oneeighth inch wide, and about five thirty-seconds inch thick may beformed suitably by introducing about 3,500 stones of mesh size -45 60grit or about 1.1 carats of diamond grit. The abrader will be in theform suitable to be mounted by brazing to a saw blade as shown in FIG.6.

Instead of metal coated tungsten carbide, we may use another metalcoated secondary abrasive described above, for example, metal coatedalumina or silicon carbide as described above.

Instead of using the low temperature melting bronze as in Examples 6 and7, we may use the higher melting metals as binder matrix such as iron,cobalt, nickel or alloys of these metals and heat the hot press mold totemperatures as high as above l,5 35 F. depending on the melting pointof the metal selected to form the binder.

In producing the encapsulated abrasives employed in the processes ofExamples 7 and 8, we prefer to employ the process of encapsulationdescribed in Example 2 and where diamonds are referred to we prefer,where they are synthetic diamonds having a smooth face, that this beetched, for example, by the procedure of Example 1.

The superior product produced by the encapsulation method of Examples 1and 2 when used in the production of the abraders by the hot press orinfiltrant method is illustrated in FIG. 7 which shows a 0.025 inchtungsten coat on an alumina particle in the metal matrix at 140 Xmagnification.

FIG. 8 shows a similar tungsten coated alumina particle in a metalmatrix at 280 X magnification.

FIG. 9 shows a micron tungsten coated diamond particle hot pressed intoa metal matrix at 210 X magnification and FIG. 10 shows a portion of theparticle at 840 X magnification.

FIG. 1 1 shows -80 100 mesh silicon carbide particle coated withtungsten, hot pressed into a metal matrix at 280 X magnification.

FIG. 12 shows tungsten coated A1 0 hot pressed in a metal matrix atl,700 polished and etched to show the allotriomorphic dendrite crystals.2 It will be seen the excellent throwing power of the process and theintimate coating produced. The metal sheath is congruent to thesubstrate surface coproducing it faithfully. The resultant intimate bondproduces the advantages of compression and hot transfer referred toabove.

The cyystal forms will be seen to be allotriomorphic with theinterlocked dendrites as described above.

We claim:

1. A shaped abrader comprising a continuous phase of a metal matrix,primary abrasive particles and secondary abrasive particles, saidprimary and secondary abrasive particles being of different densities,the primary abrasive particles having a hardness more than 2,000 kg/mmand said secondary abrasive particles having a hardness of above about1,250 kg/rnm and less than the hardness of the primary abrasiveparticles, the particles of lower density, being encapsulated in a metalenvelope, the densities of said encapsulated particles of lower densitybeing greater than the density of the unencapsulated particles of lowerdensity, said encapsulated particles having a density more than 30percent of the density of highest density, and said particles beingsubstantially uniformly distributed in said metal matrix.

2. The abrader of claim 1 in which said primary abrasive is diamond andsaid secondary abrasive is an inorganic-compound having a hardness of atleastabout 1,250 kg/mm. 7

3. The abrader of claim 1 in which the encapsulating metal is chosenfrom the group consisting of tungsten, tantalum, columbiurn, molybdenumand titanium.

4. In the abrader of claim 1 in which the-secondary abrasive is metalencapsulated with a member of the group consisting of tungsten carbideand alumina and silicon carbide. I

5. In'the abrader of claim 4 in which the primary abrasive is metalencapsulated diamonds and the secondary abrasive is a member of thegroup consisting of metal encapsulated tungsten carbide, metal encapswlated alumina and metal encapsulated silicon carbide.

6. In the abrader of claim 1 in which the primary abrasive is diamondencapsulated with a metal and the secondary abrasive is aluminaencapsulated with a metal.

7. The abrader of claim 1 in which the primary abrasive is diamondencapsulated with tungsten and the secondary abrasive is tungstencarbide.

8. The abrader of claim 1 in which the primary abrasive is diamondencapsulated with tungsten and the secondary abrasive is aluminaencapsulated with tungsten.

9. The abrader of claim 1 in which the primary abrasive is diamondencapsulated with tungsten and the secondary abrasive is silicon carbideencapsulated with tungsten.

10. The abrader of claim 1 in which the primary abrasive is diamondencapsulated with tungsten and the secondary abrasive is tungstencarbide encapsulated with a metal having a specific gravity less thanthe specific gravity 'of the tungsten'carbide.

11. The abrader of claim 10 in which the metal encapsulating thetungsten carbide is a metal having a specific gravity less than l5.

12. The abrader of claim 11 in which the metal encapsulating saidtungsten carbide is chosen from the group consisting of molybdenum,columbium, and titamum.

13. In a hot press process for producing a shaped abrasive in which anintimate mixture of primary and secondary abrasive particles and apowderedmetal is positioned in a mold which is heated and subjected toelevated pressure on said mixture, the improvement in which saidparticles are composed of a primary abrasive having a hardness of aboveabout 2,000 kg/mm and said secondary abrasive particle having a hardnessin excess of about 1,250 kglmm and less than the hardness of the primaryabrasive particles, the primary abrasive particles'having a differentspecific gravity from the specific gravity of the secondary abrasiveparticles, the primary or the secondary abrasive particles beingencapsulated in a metal envelope, the densities of the encapsulatedparticles of lower density being more than 30 percent of the density ofthe particles of highest density and said particles being substantiallyuniformally distributed in said metal matrix.

14. In the process of claim 13 in which said primary abrasive is diamondand said secondary abrasive is an inorganic compound having a hardnessof at least about 2,000 kglmm 15. In the process of claim 13 in whichthe encapsulating metal is chosen from the group consisting of tungsten,or tantalum, columbium (niobium) molybdenum and titanium.

16. In the process of claim 13 in which the secondary abrasive is chosenfrom the group consisting of metal encapsulated tungsten carbide metalencapsulated alumina and metal encapsulated silicon carbide.

17. In the process of claim 13 in which the primary abrasive is metalencapsulated diamonds and the secondary abrasive is chosen from thegroup consisting of metal encapsulatedtungsten carbide, metalencapsulated alumina and metal encapsulated silicon carbide.

abrasive is diamond encapsulated with tungsten and the secondaryabrasive is alumina encapsulated with tungsten.

22. In the process of claim 13 in which the primary abrasive is diamondencapsulated with tungsten and the secondary abrasive is tungstencarbide encapsulated with a metal having a specific gravity less thanthe specific gravity of the tungsten carbide.

23. In the process of claim 13 in which the metal encapsulating thetungsten'carbide is a metal having a specific gravity less than 15.

24. In the process of claim 13 in which the encapsulating metal ischosen from the group consisting of molybdenum, columbium, and titanium.

3- ufil rm) STATES PATI'JN'L OIEFJLCE CER'l l FlCATE O I CORRECTION mmNo. 3,841,852 Dot-ed October 15, 1974 0 v mantel-(S) ARTHUR G. WILDERand HAROLD c. BRIDWELL-' It is certified that error a ppears in theabove-identified patent. .nd that said Letters Patent are herebycorrected as shown below:

a Column 5, llne. 52 ."tri morphio:" should read tr iomorphic line 63':-"voilat ile" should read "volatile- I Column line 44 "dist-rup itiye"sbouldread e-di'sruptive--; I line 461: 'unericapuslated" sl'lould read.

--urrehc spsula ted-- I Column 9,- line 9:-- "encas-u lat ed" shouldread renc"a psulat'ed-- line 26' start new paragraph beginrlin'g with Fi2 1s-- I I Colulnn ll, line ll:' after "and" insert --on-'-- line- 22: I"1,200" shoold read -4-1,25o

Column 12, line 2'8: ou'slyussd" should read --ouslj used- Si ned end!:sealed this 7th dai of January 1975.

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner -ofPatents

1. A SHAPED ABRADER COMPRISING A CONTINUOUS PHASE OF A METAL MATRIX,PRIMARY ABRASIVE PARTICLES AND SECONDARY ABRASIVE PARTICLES, SAIDPRIMARY AND SECONDARY ABRASIVE PARTICLES BEING OF DIFFERENT DENSITIES,THE PRIMARY ABRASIVE PARTICLES HAVING A HARDNESS MORE THAN 2,000 KG/MM2,AND SAID SECONDARY ABRASIVE PARTICLES HAVING A HARDNESS OF ABOVE ABOUT1,250 KG/MM2 AND LESS THAN THE HARDNESS OF THE PRIMARY ABRASIVEPARTICLES, THE PARTICLES OF LOWER DENTISY, BEING ENCAPSULATED IN A METALENVELOPE, THE DENSITIES OF SAID ENCAPSULATED PARTICLES OF LOWER DENSITYBEING GREATER THAN THE DENSITY OF THE UNENCAPSULATED PARTICLES OF LOWERDENSITY, SAID ENCAPSULATED PARTICLES HAVIG A DENSITY MORE THAN 30PERCENT OF THE DENSITY OF HIGHEST DENSITY, AND SAID PARTICLES BEINGSUBSTANTIALLY UNIFORMLY DISTRIBUTED IN SAID METAL MATRIX.
 2. The abraderof claim 1 in which said primary abrasive is diamond and said secondaryabrasive is an inorganic compound having a hardness of at least about1,250 kg/mm2.
 3. The abrader of claim 1 in which the encapsulating metalis chosen from the group consisting of tungsten, tantalum, columbium,molybdenum and titanium.
 4. In the abrader of claim 1 in which thesecondary abrasive is metal encapsulated with a member of the groupconsisting of tungsten carbide and alumina and silicon carbide.
 5. Inthe abrader of claim 4 in which the primary abrasive is metalencapsulated diamonds and the secondary abrasive is a member of thegroup consisting of metal encapsulated tungsten carbide, metalencapsulated alumina and metal encapsulated silicon carbide.
 6. In theabrader of claim 1 in which the primary abrasive is diamond encapsulatedwith a metal and the secondary abrasive is alumina encapsulated with ametal.
 7. The abrader of claim 1 in which the primary abrasive isdiamond encapsulated with tungsten and the secondary abrasive istungsten carbide.
 8. The abrader of claim 1 in which the primaryabrasive is diamond encapsulated with tungsten and the secondaryabrasive is alumina encapsulated with tungsten.
 9. The abrader of claim1 in which the primary abrasive is diamond encapsulated with tungstenand the secondary abrasive is silicon carbide encapsulated withtungsten.
 10. The abrader of claim 1 in which the primary abrasive isdiamond encapsulated with tungsten and the secondary abrasive istungsten carbide encapsulated with a metal having a specific gravityless than the specific gravity of the tungsten carbide.
 11. The abraderof claim 10 in which the metal encapsulating the tungsten carbide is ametal having a specific gravity less than
 15. 12. The abrader of claim11 in which the metal encapsulating said tungsten carbide is cHosen fromthe group consisting of molybdenum, columbium, and titanium.
 13. In ahot press process for producing a shaped abrasive in which an intimatemixture of primary and secondary abrasive particles and a powdered metalis positioned in a mold which is heated and subjected to elevatedpressure on said mixture, the improvement in which said particles arecomposed of a primary abrasive having a hardness of above about 2,000kg/mm2, and said secondary abrasive particle having a hardness in excessof about 1,250 kg/mm2, and less than the hardness of the primaryabrasive particles, the primary abrasive particles having a differentspecific gravity from the specific gravity of the secondary abrasiveparticles, the primary or the secondary abrasive particles beingencapsulated in a metal envelope, the densities of the encapsulatedparticles of lower density being more than 30 percent of the density ofthe particles of highest density and said particles being substantiallyuniformally distributed in said metal matrix.
 14. In the process ofclaim 13 in which said primary abrasive is diamond and said secondaryabrasive is an inorganic compound having a hardness of at least about2,000 kg/mm2.
 15. In the process of claim 13 in which the encapsulatingmetal is chosen from the group consisting of tungsten, or tantalum,columbium (niobium) molybdenum and titanium.
 16. In the process of claim13 in which the secondary abrasive is chosen from the group consistingof metal encapsulated tungsten carbide metal encapsulated alumina andmetal encapsulated silicon carbide.
 17. In the process of claim 13 inwhich the primary abrasive is metal encapsulated diamonds and thesecondary abrasive is chosen from the group consisting of metalencapsulated tungsten carbide, metal encapsulated alumina and metalencapsulated silicon carbide.
 18. In the process of claim 13 in whichthe primary abrasive is diamond encapsulated with a metal and thesecondary abrasive is alumina encapsulated with a metal.
 19. In theprocess of claim 13 in which the primary abrasive is diamondencapsulated with tungsten and the secondary abrasive is tungstencarbide.
 20. In the process of claim 13 in which the primary abrasive isdiamond encapsulated with tungsten and the secondary abrasive is siliconcarbide encapsulated with tungsten.
 21. In the process of claim 13 inwhich the primary abrasive is diamond encapsulated with tungsten and thesecondary abrasive is alumina encapsulated with tungsten.
 22. In theprocess of claim 13 in which the primary abrasive is diamondencapsulated with tungsten and the secondary abrasive is tungstencarbide encapsulated with a metal having a specific gravity less thanthe specific gravity of the tungsten carbide.
 23. In the process ofclaim 13 in which the metal encapsulating the tungsten carbide is ametal having a specific gravity less than
 15. 24. In the process ofclaim 13 in which the encapsulating metal is chosen from the groupconsisting of molybdenum, columbium, and titanium.